1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, more particularly to an oscillator which is principally operated in a microwave or millimetric-wave region.
2. Description of the Related Art
An oscillator composed of a semiconductor integrated circuit is well known. In the oscillator, on a substrate, there are provided a resonant circuit for generating a high-frequency signal having a predetermined frequency, and a transistor for amplifying the high-frequency signal (for example, see Japanese Laid-open Patent Publication No. 64-5206).
In the conventional oscillator of this type, it is probable that an excessive power is inputted to the transistor in an equilibrium state of oscillation causing device breakdown or deterioration of noise characteristic. Therefore, in the conventional oscillator, in general, in order to avoid these disadvantages, the small signal loop gain is decreased to achieve the equilibrium state of oscillation by a lower electric power.
As described above, in the conventional oscillator, in order to reduce the power inputted to the transistor in the equilibrium state of oscillation, the small signal loop gain is decreased to achieve the equilibrium state of oscillation by a lower power. Consequently, in the conventional oscillator, for example, the variation in characteristic to the variation in gain of the transistor is increased due to the variations in the environment temperature or manufacturing condition or the like. Thus, a countermeasure for an excessive input of the power cannot be actually achieved in many cases.